This invention relates to treating or hydrocarbon feed materials to remove sulfur, nitrogen, oxygen, metals and/or other impurities. More particularly, the invention relates to an improved treating process for hydrocarbon feeds such as petroleum and synthetic crudes in which feed is contacted with a treating gas comprising carbon monoxide and water in the presence of a steam stable catalyst comprising (1) a metallic component having activity for both watergas shift and hydrogenation reactions, (2) a support component comprising activated alumina, and (3) a steam-stabilizing phosphorous component. In a specific embodiment, the invention relates to an improved process for desulfurization of sulfur-containing hydrocarbon feeds.
It is known that hydrocarbon feeds such as petroleum and synthetic crude oils and fractions thereof can be treated to remove sulfur, nitrogen, metals and/or other contaminants by contacting the feed with a mixture of water and carbon monoxide in the presence of bifunctional or dual catalyst systems having activity for the watergas shift reaction, whereby water and carbon monoxide are shifted to product comprising molecular hydrogen, and hydrogenation activity, whereby hydrogen reacts with contaminant-containing molecules of the feed to form easily removable contaminant-containing products, e.g., H.sub.2 S, NH.sub.3. Such processes can offer advantages over typical hydrotreating processes because the need for separate hydrogen generating facilities is reduced or eliminated. U.S. Pat. No. 2,711,419 (Milbourne et al.), while primarily directed to production of fuel gas by a three-step process involving (1) reforming sulfur-containing naphtha-type feed in the presence of a nickel group catalyst promoted by a refractory oxide to form hydrogen and carbon monoxide, (2) passing product gas through a scrubber or absorber to remove sulfur and (3) methanating the sulfur-free gas, notes that some conversion of organic sulfur compounds to hydrogen sulfide takes place in the reforming step. U.S. Pat. No. 3,586,621 (Pitchford et al. '621) discloses treatment of heavy hydrocarbons to convert the same to more valuable products by contacting with steam in the presence of a barium-promoted nickel spinel catalyst (NiAl.sub.2 O.sub.4). Pitchford et al. '621 also discloses that sulfur-containing feeds can be desulfurized by contact with watergas in the presence of the above-described catalysts and that water requirements in such processes are more severe than in processes for treatment of low sulfur feeds. U.S. Pat. No. 3,676,331 (Pitchford '331) discloses a process similar to that of Pitchford et al. '621 except that the catalyst is a dual one containing a barium, calcium, strontium or magnesium carboxylate component having shift activity, and a nickel, cobalt or iron carboxylate component having hydrogenating activity. The catalysts are not used in supported form, but rather, are dissolved in the feed to be treated. U.S. Pat. No. 3,719,588 (Vernon et al.) and U.S. Pat. No. 3,728,252 (Pitchford `252) disclose similar processes wherein conventional hydrodesulfurization, hydrodenitrogenation or hydrogenation type catalysts are used.
Among the foregoing, Vernon et al. and Pitchford et al. '252 employ catalysts identical or similar to conventional hydroprocessing catalysts, thus offering advantages in terms of catalyst cost and availability as well as compatibility with typical hydroprocessing processes. Conventional hydroprocessing catalysts typically contain a metallic component having hydrogenating activity and a support component containing at least one refractory metal oxide. Metallic components based on metals of Groups VIB and VIII, and combinations thereof, have found wide use in industry owing to their activity, availability and other factors. Commercially preferred supports contain activated alumina owing to its physical strength, high surface area and pore volume, well developed pore structure and ability to interact with the metallic component to provide catalysts of improved activity and lifetime.
Despite the desirable features of activated alumina and catalysts based thereon, the use of such materials in the above-described watergas-treating processes is not entirely satisfactory due to the susceptibility of activated alumina to severe hydration in the high temperature and high steam partial pressure environment employed according to such processes. Hydration of activated alumina results in conversion thereof to the less desirable, low surface area boehmite form, swelling of catalyst particles to the point of becoming mushy, drastic losses in catalyst crush strength, plugging of process equipment, plugging of catalyst bed in fixed bed processes, loss of adequate bed expansion and catalyst mobilization in expanded bed operations, and ultimately, process failure. Of course, such problems can be avoided by appropriate replacement of catalyst; however, the frequency of replacement typically is so high that any advantage associated with reducing hydrogen generating costs via the shift reaction are lost. Accordingly, the instability of activated alumina and catalysts based thereon to steam under reaction conditions renders treating of hydrocarbon feeds with watergas impractical.
It would be desirable to improve the above-described processes in terms of catalyst stability and lifetime so that the advantages associated with generation of hydrogen by the shift reaction could be more fully exploited. It is an object of this invention to provide such an improved process. A further object is to provide an improved process for treating hydrocarbon feeds to remove contaminants, such as sulfur, nitrogen, oxygen and metals, by contact with a treating gas comprising water and carbon monoxide wherein improved catalyst lifetime and stability are attained. A more specific object is to provide an improved desulfurization process in which hydrogen requirements are reduced through the use of a treating gas comprising water and carbon monoxide and a steam-stabilized catalyst having both shift and hydrogenating activity. Other objects of the invention will be apparent to persons skilled in the art from the following description and the appended claims.
I have now found that the objects of this invention can be attained through the use of an improved catalyst composition comprising (1) a metallic component having shift and hydrogenating activity, (2) a support component comprising activated alumina, and (3) a steam-stabilizing phosphorus component in treating hydrocarbon feeds with a treating gas comprising water and carbon monoxide. Advantageously, the use of such improved catalysts in the high temperature and high steam partial pressure environment required for effective treating yields good results in terms of removal of contaminants and with improved catalyst lifetime. Further, the invented process offers advantages in that the steam-stabilized catalyst composition to be employed can be prepared by simple techniques with incorporation of the steam-stabilizing phosphorus component into the composition being possible at a variety of points during catalyst preparation.
While incorporation of phosphorus components into various catalysts and catalyst supports has been proposed for various purposes in the past, it could not have been predicted that incorporation of a phosphorus component into catalysts comprising a metallic component having shift and hydrogenating activity and a support component comprising activated alumina would have a steam-stabilizing effect sufficient to permit long term use in hydrocarbon treating processes conducted in an environment containing steam at high temperature and partial pressure. U.S. Pat. No. 3,287,280 (Colgan et al. '280) discloses that phosphoric acid residues remaining in hydrodesulfurization catalysts prepared by impregnation of alumina with phosphoric acid solution or solutions of nickel and molybdenum salts impart thermal stability to the catalysts and that on steaming at 705.degree. C. such catalysts lose less surface area then comparative catalysts prepared without use of phosphoric acid. Of course, the patentee's steaming temperature is so severe that it is difficult to predict whether use of phosphoric acid would have an appreciable effect relative to the comparative catalyst under process conditions employed according to the present invention. In any event, the patentee does not suggest that such use of phosphoric acid would lead to catalysts of improved resistance to hydration and the accompanying mushiness and losses in crush strength. Further, the patentee is silent with respect to shift activity and the effect of phosphoric acid thereon, thus clearly failing to suggest or contemplate use of a phosphorus component to steam stabilize catalysts having both shift and hydrogenating activity in order to permit long term use in hydrocarbon treating processes conducted in an environment containing steam at high temperature and partial pressure.
U.S. Pat. No. 3,403,111 (Colgan et al. '111) is directed to improving the crush strength of silica-free alumina-supported catalysts subjected to regeneration in the presence of steam. The improvement is attained by treatment of the silica-free alumina support with nitric acid prior to impregnation of active metal component precursors. There is, however, no disclosure or suggestion that a similar effect could be achieved with phosphoric acid. Further, the steam pressures to which the patentee's catalysts are subjected are less severe than those employed according to the present invention, so even if the teachings with respect to nitric acid could be extended to phosphoric acid, it could not reasonably be concluded that incorporation of a phosphorus component would lead to improved steam stability or crush strength in the environment of the present invention. Similar to Colgan et al. '280, Colgan et al. '111 is silent with respect to shift activity.
U.S. Pat. No. 3,840,472 (Colgan '472) is similar to Colgan et al. '280 in disclosing the use of phosphoric acid solutions of hydrogenating metal salts to impregnate catalyst supports. Unlike Colgan et al. '280, however, Colgan '472 is silent with respect to steam or its effects on catalyst performance or properties. Colgan '472 also is silent with respect to shift activity.
U.S. Pat. No. 3,879,310 (Rigge et al.) discloses active aluminas of improved thermal stability and utility in isomerization processes prepared by incorporation of phosphate anion into pseudoboehmitic alumina. There is no disclosure, however, with respect to steam stability, or compositions containing an active metallic component and the disclosed stabilized aluminas, or with respect to use of the patentee's alumina as a support for catalysts to be employed in processes involving both shift and hydrogenating reactions.
Other patents and publications of possible interest to the present invention are U.S. Pat. No. 2,917,532 (Watkins)--hydrotreating process involving a first stage in which hydrogen is obtained from watergas prepared by contacting water, methane and CO.sub.2 with a catalyst containing nickel, iron, cobalt, vanadium, chromium, molybdenum or copper supported on silica, alumina, zirconia or magnesia, preferably nickel on magnesia; U.S. Pat. No. 3,711,426 (Jorgensen)--high temperature shift catalyst containing lead oxide-promoted iron oxide; abstract of U.S. Pat. No. 3,740,193 (Esso)--cesium carbonate as stable shift catalyst; U.S. Pat. Nos. 3,850,840 and 3,850,841 (both Aldridge et al.)--shift catalysts containing at least one Group VB, VIB or VIII metal component and at least one alkali metal component and, optionally, a support; U.S. Pat. No. 3,974,096 (Segura et al. '096)--shift catalyst containing at least one Group VB, VIB or VIII metal component, at least one alkali metal component, halogen and, optionally, a support; U.S. Pat. No. 4,054,644 (Segura et al.)--watergas shift process using catalyst of Segura et al. '096. None of the foregoing discloses or suggests the process of the present invention.